1. Field of the Invention
The present invention relates to an air bag device including an inflator accommodated in a retainer to which a peripheral edge of an opening in a folded-up air bag is fixed, the air bag being adapted to be deployed by a gas generated by the inflator upon collision of a vehicle, and a control valve capable of opening and closing a vent hole defined in the retainer.
2. Description of the Related Art
In a conventional air bag device, a vent hole is provided in an air bag which is expanded by a gas generated by an inflator, so that a portion of the gas is discharged through the vent hole to control the internal pressure in the air bag. There is such a proposed air bag device, in which the air bag is expanded immediately at an initial stage of the deployment by previously closing the vent hole by a thin membrane and, when the deployment is completed to increase the internal pressure in the air bag, the thin membrane is broken, whereby the gas is discharged through the vent hole to softly restrain an occupant (see Japanese Utility Model Publication No.5-6206).
There is also a proposed air bag device including two inflators mounted therein, so that when no occupant exists in the vicinity of the air bag device, both of the inflators are ignited, and when an occupant exists in the vicinity of the air bag device, only one of the inflators is ignited, thereby controlling the speed of deployment of an air bag and the internal pressure in the air bag in accordance with the position of the occupant (see Japanese Patent Application Laid-open No.9-301115).
The air bag device described in Japanese Utility Model Publication No.5-6206 suffers from a problem that a dispersion in pressure is liable to be generated for breaking the thin membrane and for this reason, when an internal pressure in the air bag has reached a predetermined value, it is difficult to properly open the vent hole. Also, the vent hole, once opened, cannot be closed and hence, it is difficult to accurately control the internal pressure. The air bag device described in Japanese Patent Application Laid-open No.9-301115 suffers from a problem that the two inflators are required, resulting in not only an increase in number of parts to cause an increase in cost, but also the deployment of the air bag can be controlled only in two stages and hence, it is difficult to carry out a close control.
There is also an air bag device proposed by the present applicant, wherein a vent hole is disposed in a retainer having an inflator accommodated therein, so that the speed of deployment of an air bag and the internal pressure in the air bag are controlled closely by opening and closing the vent hole by a control valve (see Japanese Patent Application No.10-143781).
However, the air bag device proposed in Japanese Patent Application No.10-143781 suffers from the following problem: In such air bag, the control valve comprises a piezoelectric element bonded to a protector which is made of a strip-shaped metal plate and which has the same shape as the protector, so that the protector is curvedly deflected along with the piezoelectric element by supplying an electric current to the piezoelectric element to open a vent hole. For this reason the expensive piezoelectric element is increased in size, causing an increase in cost.
Accordingly, it is an object of the present invention to provide an air bag device including a control valve capable of opening and closing a vent hole disposed in a retainer, wherein the size of an actuator required for the control valve is reduced to provide a reduction in cost.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided an air bag device comprising an inflator accommodated in a retainer to which a peripheral edge of an opening in a folded-up air bag is fixed, so that the air bag is deployed by a gas generated by the inflator upon collision of a vehicle to restrain an occupant, and a control valve capable of opening and closing a vent hole disposed in the retainer, wherein the control valve includes a valve member adapted to close the vent hole, and an actuator provided on a hinge portion of the valve member, so that an electric current is supplied to the actuator operative to bend the valve member at the hinge portion, thereby opening the vent hole.
With the above arrangement, when the air bag is deployed by a high-pressure gas generated by the inflator, the opening degree of the vent hole permitting the high-pressure gas to escape is controlled by the control valve. Thus, each of the intensity of a restraining force provided by the air bag, the speed of contraction of the air bag, and the like, can be set at any value in accordance with the state of collision of the vehicle and the condition of an occupant. In addition, since the actuator is provided on the hinge portion of the valve member, the slight movement of the actuator can be enlarged to operate the valve member in a large way. Thus, the size of the actuator can be reduced to provide a reduction in cost.
According to a second aspect and feature of the present invention, in addition to the first feature, the actuator is a piezoelectric element. With this arrangement, the size of the actuator can be reduced remarkably by employment of the piezoelectric element.
According to a third aspect and feature of the present invention, in addition to the first feature, the valve member of the control valve covers the vent hole from the outside of the retainer. With such arrangement, the valve member of the control valve covers the vent hole from the outside of the retainer having the inflator accommodated therein. Therefore, even if the control valve is not opened sufficiently due to a lack of the operation or the non-operation of the actuator, the control valve can be forcibly opened by an increase in internal pressure in the retainer to prevent the internal pressure from being excessively increased.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.